Samsung’s new “enthusiast” compact, the TL500 (or EX1 outside the US) was announced at the PMA show in February; but as of this writing, it’s not yet available from the usual mainstream sources. However, reviews are starting to filter out: Both Luminous Landscape and now Photography Blog have given it very positive ratings. (DP Review has a sample gallery posted, which suggests they’ll be posting their own full rundown soon.)

Samsung TL500 (EX1)

Stout Little Fellow

As with any small-sensor compact, there’s still some image-quality compromises. The active area of the TL500′s sensor measures about 7.5 x 5.6 mm, so ISO 800 still shows obvious noise.

However this new Samsung is beginning to look like one of the better options in the “serious compact” segment. (Street prices will start out about $400, presumably to drift downwards from there—that’s higher than a Canon S90, but well below Ricoh and Leica levels.)

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Despite endless technological evolution, one photography convention has endured for more than a century: Our numbering system for lens apertures. That is, the familiar “f-stop” scale:

1.4   2   2.8   4   5.6   8   11   16   22

This sequence is admittedly peculiar-looking, and it always confuses beginners. Why do larger numbers mean smaller-diameter lens openings?

But as many of you are aware, these numbers are actually “f/ratios“—that is, they’re the ratio of a lens’s focal length to the aperture diameter. Setting a lens to f/4.0 means its aperture opening measures one-fourth of the focal length.

F-number Definition

F/Ratio Definition

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As someone who rarely photographs sports or wildlife, the world of long-zooms is not one I pay much attention to.

But there’s trouble brewing lately, in the “bridge camera” market; and it’s reached a point even I can’t ignore.

Yes, just as with megapixels, camera makers have launched another numbers race—this time over zoom range.

Currently, bragging rights go to Olympus, with their SP-800UZ (“ultrazoom,” geddit?). While it shares an alarming 30x zoom range with Fujifilm’s HS10, the Oly is biased more towards the telephoto end. And so, the SP-800UZ wins the zoom war with a zany maximum of 840e!

Olympus SP-800UZ

Olympus: My Numbers Are Biggest!

The outsized lens makes the SP-800UZ one rather odd-looking camera. And despite the SLR-ish hump on top, there is actually no eye-level viewfinder. You must frame using the back LCD—holding the camera away from you.

Now, for those who photograph birds, zoo animals, stadium sporting events, etc., I’ll admit the handiness of having a long zoom range.

But 840e is getting into crazy-magnification territory. Just locating the subject will be a challenge (especially with  unsteady arms-length viewing). For reference, we’re talking more than double the magnification you would typically buy in binoculars.

Needless to say, aggressive two-stage antishake becomes mandatory in UltraZoom cameras. Even so, you’d better pray for strong sunlight to keep shutter speeds brief. And once your subjects are really in the distance, no lens will remove the milky haze of the atmosphere itself…

Nonetheless, all the major camera makers are now cranking up their UltraZoom specs. (Panasonic is being the most conservative, with “only” 18x on their FZ35.)

The styling of UltraZooms usually mimics the serious look of a DSLR. But in fact, all of these models employ the same little trick:

The imager in these cameras is nowhere near the APS-C format found in DSLRs. In fact, it’s under 8% of their sensor area. (A so-called 1/2.3″ chip is approximately 4.6 x 6.2 mm.)

This lets camera makers scale down all the lens dimensions by the same proportions. So, a focal range that would require a bazooka-like barrel on APS-C can be made smaller than a beer can instead.

And the volume of glass required for a given lens design (and thus, its weight) shrinks even more dramatically—to almost 1/40th. You can see why camera makers became so fond of this little gimmick.

But small sensors are prone to all the curses this blog has talked to death already: Picture noise, and ugly noise-reduction; poor dynamic range; and susceptibility to diffraction blur.

Also recall that the “brightness” of a lens (its widest f/stop) is actually a ratio: f/numbers are the focal length divided by the aperture diameter.

The physical diameter of the glass limits the second number; so as you zoom in, lens brightness drops. The Olympus SP-800UZ lens specs are 5.0–150 mm focal length; f/2.8–5.6 in aperture. That’s right—you sacrifice two whole f/stops at the long end of the zoom range.

In the case of the Olympus SP-800UZ, this raises another troubling question. To cram 14 megapixels into such a small sensor, each one can only measure 1.44 microns across.

But when your lens is set at f/5.6, diffraction creates an Airy disk almost 7.6 microns wide.

So when you’re fully zoomed in, how sharp can your photo even be? The smallest point of light theoretically possible smears across a dozen pixels. And this is before considering lens aberrations (which are probably significant too, at the extremes of the zoom range).

So if an UltraZoom is what you need, don’t let me stop you from buying one.

But just don’t expect it to rewrite the laws of physics.

This year’s PMA trade show in Anaheim is over now, without much to show for itself.

To keep my life simple and my blood pressure under control, I intend to ignore all new cameras with 1/2.3″ sensors.

It’s only ones with larger, high-ISO-friendly chips that interest me.

However in that category, few actual, working products got unwrapped. I did mention the Samsung TL500 already. But otherwise, there were vague statements about future possibilities and “intentions.”

Okay, Sigma announced the DP2s and its wide-angle sister the DP1x—modest evolutions of their earlier versions. The Foveon sensors remain (larger than Four Thirds), as do their superior non-zooming lenses. But we need to wait for reviews of these models’ handling and high-ISO performance.

Sigma DP2s

Sigma's Dark Horse Contender

Samsung confirmed its lens roadmap for the NX mount. But it will be months before we see their “wide pancake” 20mm f/2.8, which is a shame. Samsung promises lenses that are “stylish and iconic,” and I’ve always wanted to be iconic. Oh wait, that was “ironic.”

Ricoh announced that soon we’ll see two more “units” for its oddball GXR system. Again, the interesting one is the non-zoomer, with an APS-C sensor, coming later this year. But its 42e normal lens is an underwhelming f/2.5. How is this supposed to sell me on the GXR system?

Hopes for any new Panasonic G-series µ4/3 bodies also failed to materialize (despite persistent rumors that something new is on the way).

An Olympus rep was bold enough to suggest that DSLR mirrors may die soon. Reflex optical viewfinders have always been a challenge for Four Thirds cameras, since the smaller image makes the groundglass so tiny. The Olympus VF-2, with 1.4 million dots of resolution, has won over some doubters to electronic viewfinders.

As for other brands joining the EVIL bandwagon, a Nikon exec coyly said that mirrorless cameras were “one solution.” Sigma dropped a mention of its “plans” to build a mirrorless system around the Foveon sensor. But the biggest buzz came from Sony’s non-functioning model of a mirrorless APS-C-sensor compact:

EVIL Sony

Sony's "Ultra-Compact Concept Model"

First, let’s be clear none of these would be compatible with Micro Four Thirds. Lenses for µ4/3 only cover an image circle of 21.65 mm. For Foveon you need 24.9mm; and for APS-C it’s 28.4mm.

So, if these other mirrorless models come to market, their options for lenses could be fragmented, with only a few manufacturer-specific choices.

The Sony lens mount shown above is clearly a dummy: There are no bayonet tabs, or electrical contacts. Yet if it keeps that shallow register distance and wide throat (seemingly about 42 mm in their mockup) it will be much friendlier to lens adapters than the Samsung NX mount. Leica lenses on an affordable APS-C sensor, anyone?

Of course Sony has a history of imposing proprietary standards on customers (think Memory Stick or MiniDisc’s ATRAC). We shouldn’t assume the camera will even turn on, if it can’t find a properly-coded Sony lens on the front.

And Sony’s concept has no control dials visible at all. Maybe it would be a touchscreen-driven interface. Meh.

There was one bright note of hope for me in this PMA however. And that’s a bit of a convergence in comments from several different photo executives.

A Samsung VP expressed surprise how many NX10 buyers were opting for the 30mm pancake, rather than the kit zoom.

Actually this doesn’t surprise me at all: In any indoor lighting, the f/2 lens is vastly preferable to the zoom (which is 2 stops slower at 30mm).

And the pancake ridiculously small. Plus, the little guy tests pretty well too.

Samsung NX10 and Pancake

Flatter, Brighter, Sharper

Meanwhile, Sigma’s chief has started seeing that in Asian markets, even non-techie consumers are buying fast primes. They want that glamorous, shallow depth of field look—even for family snaps, or blogging what they cooked last night.

And finally, Ned Bunnell (president of Pentax’s US division, and also a blogger) was quoted as saying,

“I don’t have to be paid to say this, I really enjoy our small compact cameras and I actually adore our Limited [prime] lenses. I’m not a zoom type of photographer, and so I love our 31mm, I love all of our compact lenses, because it suits the way I was trained as photographer”

and:

“[W]e are finding a lot of people who maybe are more serious photographers who have bought the K-x, and now on the forums are asking about our Limited lenses.”

Well all right then! Three different executives suddenly think prime lenses are good. (Photographers do seem to have limped along with them OK, during those first 85 years of film cameras.)

So maybe we have a groundswell on our hands: Say goodbye to chubby, dim zooms; and hello to small, perky, and bright primes!

But… er, Ned? The FA 31mm is an oversized holdout from the film era; it costs almost $1000.

Pentax FA 31mm

Not a Pancake

I can’t find a price quoted yet for Samsung’s pancake. But the µ4/3 pancakes are $280 (the f/2.8 Olympus) and $400 (the f/1.7 Panasonic).

The Sigma 30mm f/1.4 (newly-beloved of Asian moms) is $440.

So, why can’t Pentax build a small, fast “normal” for the APS-C format?

Better have a pancake and think it over.

Something About Sharpness

February 19, 2010

Once upon a time, the way photo-geeks evaluated lens quality was in terms of pure resolution. What was the finest line spacing which a lens could make detectable at all?

Excellent lenses are able to resolve spacings in excess of 100 lines per millimeter at the image plane.

But unfortunately, this measure didn’t correlate very well with our perception looking at real photos of how crisp or “snappy” a lens looked.

The problem is that our eyes themselves are a flawed optical system. We can do tests to determine the minimum spacing between details that it’s possible for our eyes to discern. But as those details become more and more finely spaced, they become less clear, less obvious—even when theoretically detectable.

The aspects of sharpness which are subjectively most apparent actually happen at slightly larger scale than you’d expect, give the eye’s pure resolution limit.

This is the reason why most lens testing has turned to a more relevant—but unfortunately much less intuitive—way to quantify sharpness, namely MTF at specified frequencies.

MTF Chart

Thinner Curves: Finer Details

An MTF graph for a typical lens shows contrast on the vertical axis, and distance from the center of the frame on the horizontal one. The black curves represent the lens with its aperture wide open. Color means the lens has been stopped down to minimize aberrations, usually to f/8 or so. (I’ll leave it to Luminous Landscape to explain the dashed/solid line distinction.)

For the moment, all I want to point out is that that there’s a thicker set of curves and a thinner set.

The thinner curves show the amount of contrast the lens retains at a very fine subject line spacings. The thicker ones represent the contrast at a somewhat coarser line spacing (That’s mnemonically helpful, at least.)

The thick curves correspond well to our subjective sense of the “snap,” or overall contrast that a lens gives. Good lenses can retain most of the original subject contrast right across the frame. Here, this lens is managing almost 80% contrast over a large fraction of the field, even wide open. Very respectable.

The thin curves correspond to a much finer scale—i.e. in your photo subject, can you read tiny lettering, or detect subtle textures?

You can see that preserving contrast at this scale becomes more challenging for an optical design. Wide open, this lens is giving only 50 or 60% of the original subject contrast. After stopping down (thin blue curves), the contrast improves significantly.

When lenses are designed for the full 35mm frame (as this one was) it’s typical to use a spacing of 30 line-pairs per millimeter to draw this “detail” MTF curve.

And having the industry choose this convention wasn’t entirely arbitrary. It’s the scale of fine resolution that seems most visually significant to our eyes.

So if that’s true… let’s consider this number, 30 lp/mm, and see where it takes us.

A full-frame sensor (or 35mm film frame) is 24mm high. So, a 30 lp/mm level of detail corresponds to 720 lines over the entire frame height.

The number “720″ might jog some HDTV associations here. Remember the dispute about whether people can see a difference between 720 and 1080 TV resolutions, when they’re at a sensible viewing distance? (“Jude’s Law,” that we’re comfortable viewing from a distance twice the image diagonal, might be a plausible assumption for photographic prints as well.)

But keep in mind that a 30 line pairs/mm (or cycles/mm in some references) means that you have a black stripe and a white stripe per pair. So if a digital camera sensor is going to resolve those 720 lines, it must have a minimum of  1440 pixels in height (at the Nyquist limit).

In practice, Bayer demosaicing degrades the sensor resolution a bit from the Nyquist limit. (You can see that clearly my test-chart post, where “40″ is at Nyquist).

So we would probably need an extra 1/3 more pixels to get clean resolution: 1920 pixels high, then.

In a 3:2 format, 1920 pixels high would make the width of the sensor 2880 pixels wide. Do you see where this is going?

Multiply those two numbers and you get roughly 5.5 megapixels.

Now, please understand: I am not saying there is NO useful or perceivable detail beyond this scale. I am saying that 5 or 6 Mp captures a substantial fraction of the visually relevant detail.

There are certainly subjects, and styles of photography, where finer detail than this is essential to convey the artistic intention. Anselesque landscapes are one obvious example. You might actually press your nose against an exhibition-sized print in that case.

But if you want to make a substantial resolution improvement—for example, capturing what a lens can resolve at the 60 lp/mm level—remember that you must quadruple, not double the pixel count.

And that tends to cost a bit of money.

Dear Panasonic,

February 17, 2010

I’m sorry I called you a crackhead, really.

It was just a little joke. Can we still be friends?

Recently, we all learned that your Lumix GH1 has the best sensor of any Micro Four Thirds camera. That’s great!

And I think the native multi-aspect-ratio feature is awesome too. (You do that nicely on several cameras, like the LX3.)

But the only way you’re letting us purchase the GH1 is in a kit with a hulking, slow superzoom. That lens sold on its own costs $850, so I’m sure this really drives up the price of the combo.

The GH1 has great HD video capabilities, and I understand that the zoom is optimized for this purpose (with quieter motors, etc.)

But but for stills photography, the GH1 also has class-leading high ISO performance. Available-light shooters would surely appreciate a smaller body that can still deliver the goods at ISO 800.

I’m one of them.

So as an alternative, why not also bundle the GH1 with your excellent 20mm f/1.7 pancake?

GH1 and Pancake

Shaky Photoshopping of GH1 and Pancake

The 20mm is over two and a half stops faster! And presumably, you could offer a GH1 kit for a lot less money then. Like $400 less.

It would also make the combo dramatically smaller and less obtrusive. And the pancake’s “wide-normal” 40e focal length is actually one I find exceptionally handy.

You might sell a few extra GH1′s that way.

sincerely,

—petavoxel

Limits To Resolution

February 8, 2010

Why jam extra megapixels into a compact camera, if its lens can’t resolve enough detail to use them?

Sampling a fuzzy image with an ever more finely-spaced pixel grid eventually stops adding information. After that, it merely balloons file sizes needlessly.

So it’s useful to check whether all of a camera’s pixels are capturing something real. Or do they simply hit a wall of lens aberrations, diffraction, and sensor noise?

I’ve had a chance to take some sample shots with the 8-megapixel Nikon Coolpix P60, using the resolution test target I posted last week. (Open a tab to remind yourself how the target is supposed to look.)

The P60 is assembled in China—perhaps even in a factory that doesn’t say “Nikon” over the door. Nonetheless, Nikon’s lens designers have an enviable reputation. And using a 9-element, 7-group design, its lens aberrations ought to be reasonably well controlled. So how well did the little Coolpix do?

As with my earlier post, I set up the target so that its squares with 40 divisions per inch match the pixel pitch of the sensor. At that magnification, ideally the camera should form an image of the 40-line target as a row of black pixels, then a row of white pixels, then black, etc.

The P60 shoots images that are 3,264 pixels wide. Dividing this by 40 tells us the subject field needs to be 81.6 inches wide overall—6 feet, 9–5/8 inches. Two reference marks at the proper spacing (black electrical tape on a sheet of plywood) helped me frame each shot with the right magnification.

Here’s a full-rez sample of what one complete test frame looks like. I turned off as many automatic settings as possible, to improve consistency (see notes* at end).

We’ll start with the best-case scenario: The lens is set at its sharpest focal length (at the wide end of the zoom range) and the target is in the center of the frame. The ISO is 80 (its lowest setting), for minimum noise. The aperture is wide open, for lowest diffraction:

f/3.6, 6.4mm focal length

200% View: f/3.6, 6.4mm focal length

Yes, this is the sharpest image I got in my tests.

While it’s startling to see the rainbow patterning in the 40-line sample, this is actually the “good” news. It means that enough resolution is being focused on the sensor for the test pattern to completely confuse the demosaicing algorithm.

We also see vertical and horizontal texture in the 50-line squares; but I believe this is “false texture” (aliasing), rather than true resolution.

(And please remember that most real-world subjects lack the kind of repeating patterns which make demosaicing totally freak out like this.)

The sharpness is not quite as good at longer focal lengths. Zooming to 14.3mm (corresponding to 81e) and backing away to maintain field size, things look like this:

f/4.1, 14.3mm f.l.

200% View: f/4.1, 14.3mm f.l.

The 50- and 40-line samples have lost most of their detail; also, the 30-line sample has begun to look a bit rougher. Note that the hairline border around the number boxes is virtually gone here—unlike the first shot which showed a hint of it.

We can also look at what happens towards the edges of the frame (where lens aberrations are generally not as well controlled). At a longer zoom setting of 23.3mm, a target at the photo’s right edge looked like this:

Edge of Frame: f/4.3, 23.3mm f.l.

Edge of Frame: f/4.3, 23.3mm f.l.

Well, there’s some rather troubling green fringing here. And even the 10-line sample has lost contrast noticeably.

But the other thing to notice  is how soft the vertical 30-line square has gotten. It’s hard to avoid the conclusion that 8 megapixels is plenty at this point; more finely-spaced pixels would not capture any additional detail.

Now, traditionally photographers have enjoyed the creative control of trading off shutter speed against aperture; e.g. using longer exposures at smaller f/stops, to yield a deeper zone of sharp focus.

And the P60 is theoretically aimed at the enthusiast end of the point & shoot market—folks who would appreciate manual controls like this.

But, in fact, its aperture is only “sort of” adjustable.

Nikon’s manual notes (somewhat cryptically),

  • Aperture: Electronically-controlled preset aperture and ND filter (–0.9 AV) selections
  • Range: 2 steps (f/3.6 and f/8.5 [W])

What happens when you “stop down” this lens is that an arm swings into place with a smaller hole in it. And after inspecting this with a magnifier, the hole does appear to be covered by a rectangle of neutral-density filter material.

Combined, the filter and the hole cut out about 2.4 f/stops worth of light. But diameter-wise, the aperture is seemingly just f/6.0 or so—not the f/8.5 stated (at the zoom wide end).

Why on earth did Nikon do this? Well, it’s because stopping down the lens increases diffraction, that’s why. (And given compact cameras’ teeny focal lengths, you rarely need more depth of field.)

Despite this throttled aperture range, we can still see diffraction having a blurring effect:

Diffraction: f/10.4 (nominal), 23.2mm f.l.

Diffraction: f/10.4 (nominal), 23.2mm f.l.

First, notice the overall drop in contrast. The 50- and 40-line samples are completely featureless. And the 30-line sample has slipped past the limit of resolution—you can no longer count all of the lines.

At this zoom setting, the (physical) aperture might measure f/7.0; this means an Airy disk more than 9 microns wide. With the P60′s sensor size, those blur disks spill across many pixels.

While sharpening by the camera’s processor can accentuate the bright peak at the center of the Airy disk, it can’t pull back detail that never existed. So, if we want the ability to close down the lens even by two stops, then a sensor with larger pixels, not smaller ones, is needed.

Note that we’ve been looking exclusively at ISO 80 here—the camera’s lowest sensitivity setting. But that’s not very realistic, considering how people actually use their cameras.

With a shirt-pocket compact, we would rarely feel like lugging around a tripod! So under anything but bright daylight, we’ll often need to use a higher ISO setting.

Fifteen years ago, films of ISO 400 were the most commonly purchased speed. So how does ISO 400 look here?

ISO 400 Test: F/4.1, 14.3mm f.l.

ISO 400 Test: F/4.1, 14.3mm f.l.

The 40-line sample does show some color tint from demosaicing; but the noise (and noise-reduction processing) are severe here. Neither the 40- or 50-line samples give any hint which direction the lines run.

The 30-line squares have once again passed the point where lines cannot be resolved completely. And there’s no sign of the hairlines bordering the number boxes.

At this level of resolution, we would hardly lose any detail if we substituted a 5 megapixel sensor of the same size. Plus in that case, each pixel would have 60% more light-gathering area—helping tame the noise.

In conclusion, the P60′s lens somewhat out-resolves the sensor under the most favorable circumstances. This is seen in the form of colored, “gritty” demosaicing artifacts.

But it doesn’t take long before real-world complications undercut the sensor’s inherent resolving power. And while we’ve treated aberrations, diffraction, and noise as separate, in practice several of these handicaps often come together in the same photograph (along with other factors such as camera shake).

This test is not definitive; it merely represents the performance of one, very average compact camera. However if we are seeing such flaws at “only” 8 megapixels, what sense does it make to drive up pixel counts even higher—to today’s 10, 12 or 14 Mp?

You can download a PDF of the target here. If you own a compact camera, I encourage you to try this test for yourself.

* Test setup: The camera was mounted on a tripod, with VR turned off. Unless noted otherwise, enlarged details are from the center of the frame, with the camera set at ISO 80 (best-case conditions).

I set ISO, aperture, and shutter speed manually. The white balance was set to “cloudy,” and the contrast setting was turned up to +1. I left sharpening and saturation at their mid setting, 0. A 2-second self-timer allowed vibrations to die out after I pressed the shutter release.

Autofocus used the central spot only; this included several of the target’s black squares. Two shots were taken at each setting, allowing the camera to re-focus each time (I never noticed any inconsistency between pairs of photos).

The 200% samples shown here were upsized using Photoshop’s “nearest neighbor” method, to avoid any additional artifacts. Any sharpening halos are from the camera’s own processing.

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